1. Field of the Invention
This invention relates to an improved guitar soundboard and, particularly, to a compression molded composite material soundboard including a woven graphite fiber, epoxy resin matrix top lamination.
2. Summary of the Background Art
Modern wood acoustic guitars have a soundboard which consists of spruce wood to the underside of which has been glued several wooden braces. The sound quality which emanates from these guitars is presently considered desirable and the standard to which any non-wood composite soundboard is presently held.
The problems related to wooden musical instruments have historically been numerous. Wood soundboards gain and lose moisture. This phenomenon may cause undesirable changes to the intonation of the instrument, as well as threatening the durability of the instrument by weakening the structure. Another problem of wood soundboards is the degree of warpage which occurs over time due to the propensity of wood to creep when subjected to tension for long periods of time. This warpage is usually evident in the bridge area where the strings are anchored, and therefore the area where high tensions are exerted upon the wood. The luthier usually deals with this problem by adding additional bracing underneath the bridge, which can detract from the sound production emanating from the guitar.
Lastly, wood has an unpredictability which is always associated with something that nature has provided. No two pieces of wood sound the same. Since the soundboard is usually fabricated from two matched pieces of wood, even the same guitar could have mixed qualities due to the nature of wood. A luthier never knows for sure how his latest creation will sound until it is completely finished.
It has been apparent in the prior art concerning composite soundboard substitutes for wooden soundboards that the designers are trying to copy the sound of wood and, thus, they are attempting various approaches which tend to reduce the composite material to some of the same physical limitations as are found in wood. As an example, U.S. Pat. No. 4,364,990 of Haines describes a soundboard which produces a sound similar to wood by sandwiching a layer of cardboard between two layers of composite material. The stated objective is to dampen the sound vibrations which would have otherwise emanated from the composite structure. One of the drawbacks of this design is the weakness created by bonding an extremely weak material in comparison between two layers of extremely strong and stiff materials. This tends to create weak areas which can encourage delamination.
The other problem is that sound production is reduced, since the damping effect will diminish all accepted descriptions of sound production.
Another approach of similar nature is U.S. Pat. No. 4,353,862 of Kaman, in which he fabricates a soundboard for a guitar by placing a sheet of wood in a shallow mold cavity with a layer of fiberglass fabric, and proceeds to spread a layer of liquid resinous compound over the fiberglass in order to impregnate fabric. The resin is cured inside a vacuum bag. The combination of wood and fiberglass along with a wet layup of resin assures a reduction in sound production called damping.
Still another approach has been recorded by Decker, et al, in U.S. Pat. Nos. 4,873,907 and 4,969,381. The composite design of Decker consists of a combination of silk cloth for visual ornamentation, graphite unidirectional fibers are added and finally a woven fabric of aramid fiber, known for its damping qualities, is applied. The resin is applied as a wet layup and is molded without the benefit of uniform pressure application. The resultant soundboard will be lacking in uniformity of fiber spacing, as well as no uniformity of percentage of fiber to resin. Also, the resin content is extremely high, at about 50%, when compared to the percentage of fiber. This creates a soundboard which has lower resonance qualities when compared to an accurately preimpregnated fiber graphite material which has an initial percentage of resin to fiber, by weight of 33% resin to 67% fiber. The excess resin, the lack of uniform temperature and pressure application, and the use of polyester resin systems, all tend to produce a weak and nonpredictable type of soundboard, with less than optimum sound production.
As illustrated by the great number of prior patents, efforts are continuously being expended in an effort to produce acoustic guitar soundboards of improved sound, which are more efficient, reliable, inexpensive and convenient to manufacture and use.
The present invention achieves its intended purposes, objectives and advantages through an unobvious combination of component elements, with the use of a minimum number of parts, at a reasonable cost to manufacture and by employing only readily available materials.
Accordingly, it is an object of the present invention to provide an improved acoustic guitar comprising a soundboard formed of an epoxy resin impregnated graphite combination which has a predesigned percentage of epoxy resin, about 33%, impregnated into a predesigned percentage of carbon fiber, about 67%. The outer layers, upper and lower, consist of a woven cloth of graphite fiber impregnated with epoxy resin. The internal layers are epoxy empregnated unidirectional graphite fobers in which each layer is placed in the ratio of approximately three to four times as many layers in the longitudinal direction as layers in the lateral direction.
The soundboard layup is then placed in a mold, if desired, and then placed in a heated platen press where uniform temperature and pressure is applied, assuring proper resin flow and squeezeout and uniform orientation of fibers so as to eliminate the chance for either an excess or an absence of resin. The combination of careful preimpregnation of the graphite fibers with the uniform application of heat and pressure assure predictability and maximum strength for the part.
The outer lamination of woven graphite fabric assures mechanical fiber placement which helps to eliminate the usual weakness apparent in unidirectional graphite when it is used on an outer surface, i.e., its propensity to delaminate in fibrous layers when a shear force is applied. These forces may be applied by the luthier during the construction stages. The mechanical interlocking design of the woven fabric also eliminates the possibility of fiber misdirection due to molding pressures prior to the curing of the part. The woven graphite fabric also produces a distinct visual appearance not previously recognized to be desirable in a guitar soundboard. The interweaving of the fiber yields an appearance of depth to the finished surface. Finishing can be accomplished with a clear surface finish similar to the surface treatments for wood.
It is a further object of the present invention to create a soundboard of carbon fibers in an epoxy resin matrix which has improved sound characteristics as compared to wood soundboards. This sound production is not inhibited by a desire to dampen and therefore the sound of graphite fibers in a matrix of epoxy resin can be explored without bias towards wooden soundboards.
It is a further object of the present invention to compression mold a soundboard utilizing a mold shape which may incorporate soundholes, radii at edges, thin grooves for decorative trim application, as well as the elimination of subsequent machining operations in order to render the soundboard to the proper final shape prior to installation onto the side walls of the guitar.
It is a further object of the present invention to compression mold a soundboard with bracing incorporated into the resultant molded part. This allows the designer to experiment with curved rather than straight line braces, which are common with wooden bracing.
It is a further object of the present invention to compression mold a soundboard of complex curvatures in order to enhance sound production. For example, due to the ability of this material to assume complex shapes the soundboard may be rounded, raised, faceted and otherwise formed in order to create resonance zones which reverberate in sympathy with pleasing sound vibration frequencies.
It is a further object of the present invention to compression mold a soundboard with wave-like undulations which may radiate inwards from the binding edges of the soundboard towards the central area. These waves enable the soundboard to more easily vibrate as the stiffer anchoring effect of the bonding of the soundboard with the side walls is partially negated by the undulations.
The foregoing has outlined some of the more pertinent objects of the present invention. These objects should be construed to be merely illustrative of some of the more prominent features and applications of the intended invention. Many other beneficial results can be attained by applying the disclosed invention in a different manner or by modifying the invention within the scope of the disclosure. Accordingly, other objects and a fuller understanding of the invention may be had by referring to the summary of the invention and the detailed description of the preferred embodiment in addition to the scope of the invention defined by the claims taken in conjunction with the accompanying drawings.